As a power supply circuit which converts electric power supplied from an AC power supply such as a commercial power supply into a DC for lighting a light-emitting element such as a light-emitting diode (to be referred to as an “LED” hereinafter) or an organic electroluminescence (to be referred to as an “organic EL” hereinafter), a combination of a power factor correction circuit and a power converter circuit is known. The power factor correction circuit is a circuit that approximates the input power factor to 1 so that the power supply distortion of the commercial power supply and the like is suppressed. As the power factor correction circuit, for example, a voltage booster circuit is employed. The power converter circuit is a constant-current drive circuit that operates to maintain a current flowing in a light-emitting element at a predetermined target value by adjusting the voltage to be applied to the light-emitting element. As the power converter circuit, for example, a system using a fly-back converter circuit, a DC/DC converter circuit, or a half-bridge circuit is employed. Usually, a load voltage which drives a light-emitting element such as an LED or organic EL is lower than an output voltage outputted by the power factor correction circuit. Hence, as the power converter circuit, a voltage-dropping type circuit that outputs a voltage lower than the input voltage is employed. Various types of power supply voltages are used as the power supply voltage of the commercial power supply. The power supply circuit, therefore, is desirably capable of coping with an AC power supply of a wide voltage range (for example, patent literatures 1 and 2).
The power supply circuit of a luminaire that consumes a certain degree of power or over is required to perform harmonic component regulation and to have a high power factor, and is accordingly formed by combining a power factor correction circuit and a power converter circuit. A forward voltage generated across the two ends of an LED when a current is supplied to the LED changes depending on variations in the manufacture, the ambient temperature, heat generation by the loss of the LED, and the amount of current supplied. Considering such variations and temperature change, to obtain a desired light-emitting output stably from a luminaire which uses an LED, it is desired to drive the LED with a constant current.
The difference between the present invention and patent literatures 3 to 13 associated to the present invention will be described hereinafter.
(1) Patent literature 3 discloses a lighting method with which power supply devices of the same specification can light lighting heads connected to the power supply devices with the rated current in accordance with the specifications of the individual lighting heads.
According to the lighting method of patent literature 3, the lighting head must incorporate a discrimination circuit, and the power supply device requires two Current control circuits, e.g., a current detection resistor and a detection resistor. Regarding this, according to the present invention, the LED series circuit need not incorporate a resistor that discriminates the specification of the element, and the power supply circuit requires only one current control circuit.
(2) Patent literature 4 discloses, in the backlight of a liquid-crystal display device, a method which drives a light-emitting diode under an optimum condition that provides a uniform brightness and chromaticity even when the drive currents for the light-emitting diodes vary.
In patent literature 4, the drive voltage is applied to the light-emitting diode from an LCD drive circuit. In contrast to this, in the present invention, since constant-current control is performed, even when the characteristics of the light-emitting elements vary, the light-emitting elements can be driven with a constant target current value. In patent literature 4, the drive condition for the light-emitting diode which is stored in advance is read in response to an external control signal. According to the present invention, the light-emitting element connected is discriminated automatically when the power supply is turned on.
(3) Patent literature 5 discloses, in an optical adapter for an endoscope device, a method of downsizing an endoscope insertion part by reducing the number of signal lines employed for checking the attached/detached state, checking the type of the optical adapter, and driving an LED.
In patent literature 5, a plurality of power supplies are prepared for the endoscope main body which are employed for checking of the attached/detached state, lighting the LED, and driving the LED. In contrast to this, the present invention requires only one power supply circuit. In patent literature 5, the signal lines from the optical adapter are switched by a switching circuit, whereas in the present invention, the line that connects a light-emitting element and the power supply circuit need not be switched. The optical adapter of patent literature 5 requires a type checking resistor, while the light-emitting element of the present invention does not require such a type checking resistor.
(4) Patent literature 6 discloses, in an endoscope device, a method capable of checking an optical adapter mounted, driving an LED in the optical adapter in a suitable manner for the structure of the LED, and reducing the diameter of an endoscope insertion part.
In patent literature 6, the types of a plurality of optical adapters having LEDs of different structures are checked using checking resistors in the optical adapters. In contrast to this, according to the present invention, the type of light source is checked by reading the load voltage output from the constant-current drive circuit. In the endoscope device of patent literature 6, a plurality of power supply circuits are used by switching, whereas the luminaire of the present invention incorporates only one power supply circuit.
(5) Patent literature 7 discloses, in an LED light source device provided with an LED light source part having light-emitting diodes which emit light of at least one emission color (for example, RGB emission), a method of maintaining the white balance by performing drive control based on prestored specific information on the LEDs.
In patent literature 7, a storage device stores the specific information on the LEDs in order to maintain the white balance of an LED drive circuit for light of at least one emission color. In contrast to this, according to the present invention, for example, in a light-emitting element using a white LED for lighting, information such as threshold values for checking the number of LEDs and drive current values are stored in a microcomputer. According to patent literature 7, white color is generated by mixing a plurality of emission colors, and the white balance of the white color is controlled. Unlike such patent literature 7, the present invention relates to a power supply circuit capable of driving a plurality of light-emitting elements with different constant-current values.
(6) Patent literature 8 discloses an LED lighting control circuit which controls an LED drive current to cope with fluctuations in VF (forward voltage) of the LED such that the output power falls within a predetermined range; and a vehicle lighting fitting.
According to patent literature 8, control is performed to suppress a change in output power by changing the value of the drive current in accordance with the value of the VF of the LED. In contrast to this, the present invention performs constant-current control, and the LED is driven by a target current value regardless of the value of the VF of the LED. The light emission output (brightness) of an LED roughly depends on the current value. Accordingly, a luminaire that requires a prescribed illuminance is driven by constant-current drive regardless of the VF, so that the brightness is maintained. The constant-current circuit is designed to be capable of driving even when the VF is high. Hence, according to the present invention, when the VF of the LED is high, the output power is high; when the VF is low, the output power is low.
(7) Patent literature 9 discloses, in an LED lighting device such as a guide light or an emergency light, a method of avoiding erroneous operation of a safety circuit without changing the threshold value of the safety circuit even when an LED light source unit is exchanged.
In patent literature 9, since a diode is connected as a voltage adjusting element to the LED light source part, the power supply efficiency decreases. The present invention does not use a voltage adjusting element, so the power supply efficiency does not decrease. In patent literature 9, the voltages of a predetermined number of LEDs are monitored. In the case of an LED short-circuiting fault, when the voltage of the LED drops to less than a threshold value, power supply to the LED light source part is stopped. In contrast to this, according to the present invention, the LED light source part is kept ON even when the light-emitting element causes a partial short-circuiting fault. Power supply is stopped when an open fault occurs. In patent literature 9, the LED power supply part has a voltage dividing resistor. With the voltage dividing resistor, the LED power supply part is discriminated, and a lighting current corresponding to the discriminated LED power supply part is acquired. In contrast to this, according to the present invention, a low current is supplied to the light-emitting element, and the load voltage value at this time is measured, thus checking the type of the light-emitting element (the number of LEDs).
(8) Patent literature 10 discloses a cross-fade type lighting control device (dimmer) in which, when lighting is to change from the current lighting to the next lighting on a stage or in a television studio, the change takes place automatically and smoothly.
Patent literature 10 relates to a lighting control device and a method of carrying out cross-fade control that realizes smooth lighting change to the next scene. In contrast to this, fade shift control of the present invention is a method relating to lighting, putting out, and lighting control (dimming) of a luminaire.
(9) Patent literature 11 discloses, in a color video door-phone device, a method that gradually increases the brightness of a night lighting LED regardless of the length of the transmission path.
In patent literature 11, the current to be supplied to the LED is gradually increased using two circuits, i.e., a current control circuit and a constant-current circuit. In contrast to this, according to the present invention, using the constant-current value table of the microcomputer, the target current value is gradually changed, so that the current flowing through the light-emitting element is smoothly changed by a single constant-current circuit.
(10) Patent literature 12 discloses a method in a portable telephone, which gradually increases the brightness of a plurality of LEDs from an OFF state at desired timings.
In patent literature 12, a predetermined-current supply circuit and a variable-current supply circuit are used in order to fade-in from an OFF state and fade-out the plurality of LEDs simultaneously. With a predetermined drive current being supplied, a variable current is further added, thus performing lighting control. In contrast to this, according to the present invention, constant-current control using a constant-current value table is conducted, so that fade-in and fade-out are performed with a single power supply circuit.
(11) Patent literature 13 discloses a lighting control (dimming) method in a stage-use lighting controller (dimmer) provided with a signal reception-side lighting means which anticipates a time period that will lapse before next signal reception and performs lighting control to reach the anticipated target value stepwise within the anticipated time period.
According to patent literature 13, the signal is updated only slowly with a maximum update period of 1 sec due to the standard of the lighting control (dimming) signal. This speed cannot catch up with the lighting response speed of the LED. Hence, flickering is eliminated by anticipating the value of the next lighting control signal. In contrast to this, the present invention uses a lighting controller which is usually employed in a luminaire. The lighting control signal of the lighting controller has a frequency of about 100 Hz to 1 kHz. With this frequency, flickering to the human eye caused by the lighting control signal update period will not occur easily. According to the present invention, even when the lighting control signal changes sharply, the target current value is not changed at a rate exceeding a predetermined rate. This function is realized by conducting control that delays the change using the microcomputer, instead of anticipating the next lighting control signal value as in patent literature 13.